In various situations, people who have authority or control over a subject (e.g., an animal, a machine, another person, etc.) implement physical boundaries and markers to confine the subject to a particular geographical area. For example, animal fences (e.g., electric dog fences that have electric wires either above or below ground, fences for keeping livestock grazing within a particular area, etc.) may be used to confine animals to the property of the animal's owner, boundary markers may be used to facilitate movement of automated machines (e.g., robotic lawnmowers, farming equipment, etc.) operating within an area such as a yard or field, and physical fences and signs may be used to urge human beings to stay in a particular area (e.g., children within a schoolyard, parolees on house arrest within their premises, runners or bikers to a designated race route, etc.). While such physical boundaries and markers may be effective in confining subjects to particular geographic areas, these physical constructs may be unsightly, expensive, inconvenient, and/or difficult to move or modify.